Bandgap reference circuits are used in systems That require a reference voltage that is relatively accurate and stable. A bandgap reference circuit generally includes two p-n junctions operating at different current densities. The circuit may produce a reference voltage calculated by summing a voltage across one of the junctions with a scaled difference of the voltages across both junctions. Since each junction voltage is inversely proportional to temperature and the scaled difference is directly proportional to temperature, the sum is temperature independent. In a conventional Brokaw bandgap reference circuit, the foregoing voltages are achieved by forcing a current through two bipolar transistors with different emitter areas.
Even though bandgap reference circuits are generally considered to be accurate, mechanical and/or environmental stresses (e.g., caused by circuit packaging and mounting, temperature variations, oxidation, etc.) may cause non-uniformities and voltage instability over time. Accordingly, circuit designers have sought to compensate for such stress-induced inaccuracies.
To reduce sensitivity to package stress, most high-performance voltage references are packaged in expensive open cavity hermetic packages such as ceramic or metal can. Other solutions include implementing a stress gauge using a MOS (metal-oxide-semiconductor) device, or suspending a voltage reference core on a micro-machined membrane. These mechanisms have not produced a consistent stress response, and generally cannot compensate for unstable input signals.